<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <div></div>

    <input type="text">

    <button disabled>111</button>

    <input type="checkbox" checked>

    <select name="" id="b">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
    </select>

    <!-- <select name="" id="b">
        <option>+</option>
        <option>-</option>
        <option>*</option>
    </select> -->

    <button id="c">计算</button>

    <script>

        // 表单上的特殊属性
        //    disabled  ->   true / false     
        //    checked   ->   true / false
        //    
        // select使用的时候   option 的  value 要么删除，要么必须写值 

        var oInp = document.querySelector('input');
        console.log(oInp.disabled);

        setTimeout(function () {
            oInp.disabled = true;
        }, 2000)


        var oBtn = document.querySelector('button');

        oBtn.disabled = false;



        c.onclick = function () {
            console.log(b.value);
        }

    </script>

</body>

</html>